This invention relates to spectroscopic analysis and more particularly to spectroanalytical systems of the polychromator type.
In spectroscopic analytical techniques using emission sources such as a high voltage spark source or an arc source, material from the sample to be analyzed is introduced into an analytical region and excited to spectroemissive levels sufficient to emit detectable radiation characteristic of elements in the sample. Excitation may be by a spark or arc discharge or by plasma, alone or with supplemental excitation, or otherwise. The resulting emitted radiation typically is dispersed and analyzed spectroscopically to quantitatively determine elemental compositions of sample materials. Such techniques are useful in analyzing metals and metal alloys, for example.
In accordance with one aspect of the invention, there is provided a spectroanalytical system with radiation dispersing apparatus having dispersing structure for dispersing radiation into a spectrum for concurrent application to an exit port; a radiation sensor channel circuit that is optically coupled to the exit port for monitoring radiation at that exit port; sample excitation apparatus for exciting sample material to be analyzed to spectroemissive levels for generating a beam of radiation for dispersion by the dispersing structure; and controller structure for triggering the excitation apparatus to excite the sample material and for generating a gating interval by the channel circuitry for accumulating radiation data during an interval that commences subsequent to application of maximum energy to the sample by the excitation apparatus.
In preferred embodiments, the radiation dispersing apparatus includes polychromator apparatus with entrance slit structure, exit slit structure composed of a series of exit slit elements disposed along a Rowland circle, each exit slit element defining an exit port, and the dispersing structure is disposed between the entrance and said exit slit structures. The controller structure times the gating interval from the excitation triggering and initiates the gating interval at least thirty microseconds subsequent to application of maximum energy to the sample by the excitation apparatus.
In a particular embodiment, the excitation apparatus includes arc stand structure with counter electrode structure for applying an electric discharge to sample material to be analyzed; a trigger gap connected to the counter electrode through a spark modification circuit, and the controller structure includes means for generating a control signal to fire the trigger gap, the sample excitation apparatus being adapted to generate an electrical discharge with a maximum amplitude of at least ten amperes and a duration of less than one millisecond for application to sample material to be analyzed. An input control is connected to the controller structure and the controller structure includes a gate start register and a gate interval register, each of which is a multi-bit register that is set by signals from the input control for controlling the start and duration of the gating interval. The sample excitation apparatus includes charging circuitry, discharge circuitry, a low voltage capacitor connected between the charging and discharging circuitry and switchable between different capacitor values; a resistor switchable between different resistance values; and an inductance switchable between different inductance values, the resistor and inductance being connected to the discharge circuitry. Each channel circuit includes a photomultiplier tube that produces an output current as a function of radiation passing through its exit port, an operational amplifier for transforming the output current to a voltage, an integrator that has a capacitor in its feedback path, a first switch responsive to a signal from the controller for applying the voltage from the operational amplifier to the integrator so that when the first switch is closed, the output voltage of the integrator is proportional to the integral of the photomultiplier current, a storage register, an analog to digital converter connected to the storage register, and a second switch responsive to a signal from the controller for connecting the output of the integrator to the analog to digital converter for conversion of the value stored in the integrator to digital form for application to the storage register.
In accordance with another aspect of the invention, there is provided a method of spectroanalysis comprising the steps of exciting sample material to be analyzed to spectroemissive levels with excitation apparatus to generate a beam of radiation; dispersing the beam of radiation into a spectrum for concurrent application to a plurality of exit ports; monitoring radiation at each exit port with channel circuitry corresponding to each exit port; triggering the excitation apparatus to excite the sample material; and generating a gating interval that commences subsequent to application of maximum energy to the sample material by the excitation apparatus for accumulating data on radiation monitored by the channel circuitry during the gating interval. Preferably, the method includes the steps of generating a first signal to trigger the excitation apparatus and a second signal times and coordinated with the first signal to initiate the gating interval at least thirty microseconds subsequent to application of maximum energy to the sample by the excitation apparatus.
In accordance with another aspect of the invention, there is provided a spectroanalytical system with radiation dispersing apparatus for dispersing radiation into a spectrum for concurrent application to a plurality of exit ports; a plurality of radiation sensor channel circuits, each circuit being optically coupled to a corresponding exit port for monitoring radiation at that exit port; sample excitation apparatus for exciting sample material to be analyzed to spectroemissive levels for generating a beam of radiation for dispersion by the dispersing structure, the excitation apparatus including arc stand structure with counter electrode structure for applying an electric discharge to sample material to be analyzed, a trigger gap connected to the counter electrode through a spark modification circuit, and the controller structure includes means for generating a control signal to fire the trigger gap, the sample excitation apparatus being adapted to generate an electrical discharge with a maximum amplitude of at least ten amperes and a duration of less than one millisecond for application to sample material to be analyzed. Preferably, the sample excitation apparatus includes charging circuitry, discharging circuitry, a low voltage capacitor connected between the charging and discharging circuitry and switchable between different capacitor values; a resistor switchable between different resistance values; and an inductance switchable between different inductance values, the resistor and inductance being connected between the discharging circuitry and the counter electrode.
In accordance with another aspect of the invention, there is provided a spectroanalytical system with radiation dispersing apparatus for dispersing radiation into a spectrum for concurrent application to a plurality of exit ports; a plurality of radiation sensor channel circuits; sample excitation apparatus for exciting sample material to be analyzed to spectroemissive levels for generating a beam of radiation for dispersion by the dispersing apparatus; and controller structure for triggering the excitation apparatus to excite the sample material and for generating a gating interval by the channel circuits for accumulating data on the dispersed radiation. Each channel circuit is optically coupled to a corresponding exit port for monitoring radiation at that exit port. An input control is connected to the controller structure and the controller structure includes a gate start register and a gate interval register, each of which is a multi-bit register that is set by signals from the input control for controlling the start and duration of the gating interval. Preferably, each channel circuit includes a photomultiplier tube that produces an output current as a function of radiation passing through its exit port, an operational amplifier for transforming the output current to a voltage, an integrator that has a capacitor in its feedback path, a first switch responsive to a signal from the controller for applying the voltage from the operational amplifier to the integrator so that when the first switch is closed, the output voltage of the integrator is proportional to the integral of the photomultiplier current, a storage register, an analog to digital converter connected to the storage register, and a second switch responsive to a signal from the controller for connecting the output of the integrator to the analog to digital converter for conversion of the value stored in the integrator to digital form for application to the storage register.